Commit 64033892 authored by Neal Cardwell's avatar Neal Cardwell Committed by David S. Miller

tcp: use windowed min filter library for TCP min_rtt estimation

Refactor the TCP min_rtt code to reuse the new win_minmax library in
lib/win_minmax.c to simplify the TCP code.

This is a pure refactor: the functionality is exactly the same. We
just moved the windowed min code to make TCP easier to read and
maintain, and to allow other parts of the kernel to use the windowed
min/max filter code.
Signed-off-by: default avatarVan Jacobson <vanj@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarNandita Dukkipati <nanditad@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarSoheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent a4f1f9ac
...@@ -19,6 +19,7 @@ ...@@ -19,6 +19,7 @@
#include <linux/skbuff.h> #include <linux/skbuff.h>
#include <linux/win_minmax.h>
#include <net/sock.h> #include <net/sock.h>
#include <net/inet_connection_sock.h> #include <net/inet_connection_sock.h>
#include <net/inet_timewait_sock.h> #include <net/inet_timewait_sock.h>
...@@ -234,9 +235,7 @@ struct tcp_sock { ...@@ -234,9 +235,7 @@ struct tcp_sock {
u32 mdev_max_us; /* maximal mdev for the last rtt period */ u32 mdev_max_us; /* maximal mdev for the last rtt period */
u32 rttvar_us; /* smoothed mdev_max */ u32 rttvar_us; /* smoothed mdev_max */
u32 rtt_seq; /* sequence number to update rttvar */ u32 rtt_seq; /* sequence number to update rttvar */
struct rtt_meas { struct minmax rtt_min;
u32 rtt, ts; /* RTT in usec and sampling time in jiffies. */
} rtt_min[3];
u32 packets_out; /* Packets which are "in flight" */ u32 packets_out; /* Packets which are "in flight" */
u32 retrans_out; /* Retransmitted packets out */ u32 retrans_out; /* Retransmitted packets out */
......
...@@ -671,7 +671,7 @@ static inline bool tcp_ca_dst_locked(const struct dst_entry *dst) ...@@ -671,7 +671,7 @@ static inline bool tcp_ca_dst_locked(const struct dst_entry *dst)
/* Minimum RTT in usec. ~0 means not available. */ /* Minimum RTT in usec. ~0 means not available. */
static inline u32 tcp_min_rtt(const struct tcp_sock *tp) static inline u32 tcp_min_rtt(const struct tcp_sock *tp)
{ {
return tp->rtt_min[0].rtt; return minmax_get(&tp->rtt_min);
} }
/* Compute the actual receive window we are currently advertising. /* Compute the actual receive window we are currently advertising.
......
...@@ -387,7 +387,7 @@ void tcp_init_sock(struct sock *sk) ...@@ -387,7 +387,7 @@ void tcp_init_sock(struct sock *sk)
icsk->icsk_rto = TCP_TIMEOUT_INIT; icsk->icsk_rto = TCP_TIMEOUT_INIT;
tp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT); tp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
tp->rtt_min[0].rtt = ~0U; minmax_reset(&tp->rtt_min, tcp_time_stamp, ~0U);
/* So many TCP implementations out there (incorrectly) count the /* So many TCP implementations out there (incorrectly) count the
* initial SYN frame in their delayed-ACK and congestion control * initial SYN frame in their delayed-ACK and congestion control
......
...@@ -2879,67 +2879,13 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked, ...@@ -2879,67 +2879,13 @@ static void tcp_fastretrans_alert(struct sock *sk, const int acked,
*rexmit = REXMIT_LOST; *rexmit = REXMIT_LOST;
} }
/* Kathleen Nichols' algorithm for tracking the minimum value of
* a data stream over some fixed time interval. (E.g., the minimum
* RTT over the past five minutes.) It uses constant space and constant
* time per update yet almost always delivers the same minimum as an
* implementation that has to keep all the data in the window.
*
* The algorithm keeps track of the best, 2nd best & 3rd best min
* values, maintaining an invariant that the measurement time of the
* n'th best >= n-1'th best. It also makes sure that the three values
* are widely separated in the time window since that bounds the worse
* case error when that data is monotonically increasing over the window.
*
* Upon getting a new min, we can forget everything earlier because it
* has no value - the new min is <= everything else in the window by
* definition and it's the most recent. So we restart fresh on every new min
* and overwrites 2nd & 3rd choices. The same property holds for 2nd & 3rd
* best.
*/
static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us) static void tcp_update_rtt_min(struct sock *sk, u32 rtt_us)
{ {
const u32 now = tcp_time_stamp, wlen = sysctl_tcp_min_rtt_wlen * HZ; struct tcp_sock *tp = tcp_sk(sk);
struct rtt_meas *m = tcp_sk(sk)->rtt_min; u32 wlen = sysctl_tcp_min_rtt_wlen * HZ;
struct rtt_meas rttm = {
.rtt = likely(rtt_us) ? rtt_us : jiffies_to_usecs(1), minmax_running_min(&tp->rtt_min, wlen, tcp_time_stamp,
.ts = now, rtt_us ? : jiffies_to_usecs(1));
};
u32 elapsed;
/* Check if the new measurement updates the 1st, 2nd, or 3rd choices */
if (unlikely(rttm.rtt <= m[0].rtt))
m[0] = m[1] = m[2] = rttm;
else if (rttm.rtt <= m[1].rtt)
m[1] = m[2] = rttm;
else if (rttm.rtt <= m[2].rtt)
m[2] = rttm;
elapsed = now - m[0].ts;
if (unlikely(elapsed > wlen)) {
/* Passed entire window without a new min so make 2nd choice
* the new min & 3rd choice the new 2nd. So forth and so on.
*/
m[0] = m[1];
m[1] = m[2];
m[2] = rttm;
if (now - m[0].ts > wlen) {
m[0] = m[1];
m[1] = rttm;
if (now - m[0].ts > wlen)
m[0] = rttm;
}
} else if (m[1].ts == m[0].ts && elapsed > wlen / 4) {
/* Passed a quarter of the window without a new min so
* take 2nd choice from the 2nd quarter of the window.
*/
m[2] = m[1] = rttm;
} else if (m[2].ts == m[1].ts && elapsed > wlen / 2) {
/* Passed half the window without a new min so take the 3rd
* choice from the last half of the window.
*/
m[2] = rttm;
}
} }
static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag, static inline bool tcp_ack_update_rtt(struct sock *sk, const int flag,
......
...@@ -464,7 +464,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk, ...@@ -464,7 +464,7 @@ struct sock *tcp_create_openreq_child(const struct sock *sk,
newtp->srtt_us = 0; newtp->srtt_us = 0;
newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT); newtp->mdev_us = jiffies_to_usecs(TCP_TIMEOUT_INIT);
newtp->rtt_min[0].rtt = ~0U; minmax_reset(&newtp->rtt_min, tcp_time_stamp, ~0U);
newicsk->icsk_rto = TCP_TIMEOUT_INIT; newicsk->icsk_rto = TCP_TIMEOUT_INIT;
newtp->packets_out = 0; newtp->packets_out = 0;
......
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